1. Field of the Invention
The present invention relates generally to machines for forming glassware articles from gobs of molten glass and in particular to electronically controlled individual section glassware forming machines.
2. Description of the Prior Art
The individual section or IS glassware forming machine is well known and includes a plurality of sections each having means for forming glassware articles in a timed, predetermined sequence of steps. Typically, each section includes a blank mold station for receiving gobs of molten glass at a predetermined rate and for forming partially formed articles of glassware. A partially formed article of glassware of the type produced by the blank mold is typically referred to as a parison. The parison is then transferred to a blow mold station wherein the formation of the glassware article is completed. The sections are operated in synchronism at a relative phase difference such that one section is receiving a gob while another section is delivering a finished glassware article to a conveyor and one or more other sections are performing various ones of the intermediate forming steps.
The forming means in each section are typically operated from pneumatic motors or actuators. In early prior art machines, the pneumatic motors were controlled by a valve block which in turn was controlled by a timing drum for each section driven from a line shaft which synchronized all parts of the machine. One of the limitations of the timing drum was the difficulty of adjusting the timing during the operation of the machine. One solution to this problem was to replace all the timing drums with an electronic control means. The electronic control means included a master unit which was responsive to a clock pulse generator and a reset pulse generator driven by the line shaft. The master unit generated reset signals to an individual control circuit for each of the individual sections to synchronize the operation of the individual circuits. Each individual circuit included a pulse counter responsive to the clock pulses and the master unit generated reset pulses for counting the degrees of the section cycle. Each individual circuit included forty-eight, three-decade thumbwheel switches for setting the degree of rotation of the machine thereon. Thus, each particular function of the glassware forming cycle was controlled by one of the thumbwheel switches. Such a control system is disclosed in U.S. Pat. No. 3,762,907.
The previously described electronic control system utilized discrete components in its counter and gating circuitry. In a later prior art control apparatus, a digital computer with a memory and associated program storage was utilized. Not only did such a control circuit provide a means for automatically changing the timing values of the functions without the manual resetting of thumbwheel switches, but such a circuit also provided a means for programming events, groups of related functions, in accordance with certain boundary event timings. The computer generated control signals through an interface circuit to actuate solenoid controlled valve blocks. Such a control system is disclosed in U.S. Pat. No. 3,905,793.
One of the problems associated with the aforementioned prior art glassware forming machines occurred when one of the machine sections was producing a malformed article of glassware. It was often difficult to determine whether the malformation occurred in the blank mold station or in the blow mold station. If the parison produced by the blank station was examined before introduction to the blow mold, any defects which were observed could not be attributed to the blow station. In order to produce a parison which was sufficiently frozen to be handled and examined, the valves of the particular section had to be manually actuated to allow the parison to remain in the blank mold for an extended time such that it became sufficiently frozen. This method of producing a frozen parison sample was time consuming and consequently resulted in a drastic loss in production time.